Touch sensitive devices have become an increasingly common way for users to interact with electronic systems, typically those that include tablets, touch phones, and other commercial touch interactive systems. Touch sensitive devices allow a user to conveniently interface with electronic systems and displays by reducing or eliminating the need for mechanical buttons, keypads, keyboards, and pointing devices. For example, a user can carry out a complicated sequence of instructions by simply touching an on-display touch screen at a location identified by an icon.
There are several types of technologies for implementing a touch sensitive device including, for example, resistive, infrared, capacitive, surface acoustic wave, electromagnetic, near field imaging, etc. Capacitive touch sensing devices have been found to work well in a number of applications. In many touch sensitive devices, the input is sensed when a conductive object in the sensor is capacitively coupled to a conductive touch implement such as a user's finger. Generally, whenever two electrically conductive members come into proximity with one another without actually touching, a capacitance is formed therebetween. In the case of a capacitive touch sensitive device, as an object such as a finger approaches the touch sensing surface, a tiny capacitance forms between the object and the sensing points in close proximity to the object. By detecting changes in capacitance at each of the sensing points and noting the position of the sensing points, the sensing circuit can recognize multiple objects and determine the characteristics of the object as it is moved across the touch surface.
Capacitive touch sensitive devices often include layers of patterned transparent conductors as sensing elements. The patterned transparent conductors often include arrays of long, narrow transparent conductive electrodes in the form of rows and columns. Electrical contacts are established between the controller and the transparent electrodes by providing a conductive metal pattern. In one known method, flexible printed circuits (FPC) are directly bonded to the tail portions of the transparent conductors using anisotropic conductive film (ACF) bonding. In another known method, conductive metal patterns and bonding pads are provided to each transparent electrode by printing methods. For example, conductive inks are applied on the transparent conductors and fired to create the conductive traces on the tail portions of the transparent electrodes.
FPC and ACF bonding processes are expensive and involve high cycle time. Conductive ink printing methods require a large non-sensing area of the sensor because of limitations in providing fine pitch by the conductive ink printing process. Moreover, the higher firing temperature leads to reliability problems such as, e.g., cracks in indium tin oxide (ITO) and haze formation from the base film.
To get a matrix type sensor, row electrodes and column electrodes are laminated in orthogonal direction using optically clear adhesive. Precise alignment is important between the row and column electrodes which otherwise would result in low yield. Moreover, the formation of bubbles and air gaps is unavoidable during the lamination process. Layers of row and column electrodes together with optically clear adhesive and base polyester film may result in a thick sensor.